Beldar reminds us of the two great accomplishments of George W. Bush's national security policy. I have nothing to add to the first, which affects me personally, but I would underline the second:
[E]ven if the Iraq War did nothing else (a proposition I reject), ... it emphatically demonstrated to every other country in the world that, in their dealings with the United States, there simply is no "military solution" which can favor them.
This can't be emphasized often enough in discussing the deterrent effect of the war. Yes, the war has been hard at times on the U.S., but it is not lost on other regimes how badly it ended for Saddam, his sons and his senior apparatchiks. Or for Zarqawi or other leaders of the foreign forces opposing us in Iraq. That's a huge distinction from how Vietnam ended for Ho's regime. Only the Iranians have really come out of this well, and only because they have not yet provoked us to the point where we would turn our guns on them directly. And if the U.S. did invade and seek to conquer Iran in the same fashion as Iraq, no matter how difficult that would be for the U.S., it would be much worse for the Iranian regime.